Fresnel lens sensing system combines Fresnel lens unit and sensing unit to form a signal sensing system, wherein the Fresnel lens sense optical signals, and the sensing unit receives signals and does signal processing. Refer to FIGS. 1 and 2, the surface of Fresnel lens generally consists of concentric jagged or stepped surface, the Fresnel lens sensing signal is characterized in: long central sensing distance, big signal strength, the sharp attenuation of the sensing distance and signal strength in surrounding area. The featured light path is as shown in FIG. 1. In FIG. 2, when incident discrete angle is bigger, the dispersion of the incident signals is larger, the attenuation of the intensity is larger.
An application in monitoring system of the Fresnel lens is used to start the imaging system of the monitoring system, making the imaging system to start videoing and photographing only when the object motion is detected, resulting in reducing data amount and decreasing the power consumption of the system.
The Fresnel lens sensing system is mainly used in inspection and monitoring field, classified in two types, one type is generally to dispose a Fresnel lens unit to detect a narrow area, such as human body detection of automatic toilet, which requires the detection area to be focused on the narrow area short distance away from the front side of automatic toilet, avoiding mis-flushing operation due to mis-detection; the other type is to detect warm-blooded creatures in a certain area, the conventional design ideas of this kind of application is based on the design ideas of no blind area monitoring, which is designed to inspect every point or sub-area of the inspected area, this kind of no blind area design is realized by densely disposing a plurality of Fresnel lens units. However, the drawbacks of this dense disposition are: 1) the dense disposition may incur the area reduction of each Fresnel lens, resulting in short monitoring distance; 2) the dense disposition of Fresnel lens may incur over-sensing with very slight motion in the area, resulting in frequent photographing, the two photos in very short interval may be the same regarding the monitoring information, which actually is unnecessary and waste of resources.